Re: [RFC PATCH] dm ioctl: fix erroneous EINVAL when signaled

[Mikulas Patocka <mpatocka@redhat.com>]

Hi

I am wondering why does do_resume need to call dm_suspend at all. Does 
anyone here remember why is this code path needed?

Mikulas



On Wed, 17 Jul 2024, Khazhismel Kumykov wrote:

> do_resume when loading a new map first calls dm_suspend, which could
> silently fail. When we proceeded to dm_swap_table, we would bail out
> with EINVAL. Instead, restore new_map and return ERESTARTSYS when
> signaled.
> 
> Signed-off-by: Khazhismel Kumykov <khazhy@google.com>
> ---
>  drivers/md/dm-ioctl.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> 
> RFC as I am rather unfamiliar with the locking semantics here - whether
> we do need to re-grab hash_lock to write to an hc we previously grabbed,
> and whether the device becoming unhashed while we're in this function is
> really something that needs to be checked. However, this patch does fix
> the issue we were seeing - we'd get EINVAL when thread in ioctl was
> signaled.
> 
> 
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index c2c07bfa6471..b81650c6d096 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -1181,8 +1181,22 @@ static int do_resume(struct dm_ioctl *param)
>  			suspend_flags &= ~DM_SUSPEND_LOCKFS_FLAG;
>  		if (param->flags & DM_NOFLUSH_FLAG)
>  			suspend_flags |= DM_SUSPEND_NOFLUSH_FLAG;
> -		if (!dm_suspended_md(md))
> -			dm_suspend(md, suspend_flags);
> +		if (!dm_suspended_md(md)) {
> +			r = dm_suspend(md, suspend_flags);
> +			if (r == -EINTR)
> +				r = -ERESTARTSYS;
> +			if (r) {
> +				down_write(&_hash_lock);
> +				hc = dm_get_mdptr(md);
> +				if (!hc)
> +					r = -ENXIO;
> +				else
> +					hc->new_map = new_map;
> +				up_write(&_hash_lock);
> +				dm_put(md);
> +				return r;
> +			}
> +		}
>  
>  		old_size = dm_get_size(md);
>  		old_map = dm_swap_table(md, new_map);
> -- 
> 2.45.2.993.g49e7a77208-goog
>